Don't know if they yet offer piston systems, but might look into Rock River or DPMS. My factory gas tube Bushmaster shoots MOA off the bench. I've read alot of good things about the RR and DPMS over the years.

For ultimate accuracy and gauranteed accuracy, might check into Les Baer Custom. If I didn't already have two AR uppers, I would buy one from Les.

I am sure there are other "semi-custom" makers out there that make accurate AR's. Maybe others will respond with some names.

My "work" gun is a 10.5 inch LWRC, and it is awesome. I can't comment on the accuracy, because we've never shot them from a bench. I don't have any experience with other piston guns, but after shooting these I wouldn't bother looking at anything else.

Why do you want a piston? I have owned more than a few ARs in the last 10 years and do have a piston now just wanted to try it out. What I have come to understand is unless you are running an SBR suppressed their is no need for a piston.

Ruger's AR is piston, Rock river, DPMS/Bushmaster/Remington/S&W, Sig, and a few others offer pistons.
As much as I can't stand the Gas impingement system, it's a hell of a lot cheaper, and almost all parts ar based for it. Use clean burning powder in reloads, like Ramshot X-terminator, or TAC. I don't clean my ARs, just oil the bolt, carrier, trigger, hammer, and scrub the bore once in a while. I've never had a stoppage.

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There are only two seasons: Hunting season, and Getting Ready for Hunting season. -DAD

Ruger's AR is piston, Rock river, DPMS/Bushmaster/Remington/S&W, Sig, and a few others offer pistons.
As much as I can't stand the Gas impingement system, it's a hell of a lot cheaper, and almost all parts ar based for it. Use clean burning powder in reloads, like Ramshot X-terminator, or TAC. I don't clean my ARs, just oil the bolt, carrier, trigger, hammer, and scrub the bore once in a while. I've never had a stoppage.

This is all bad advice there is nothing wrong with the DI system and you have to clean your weapon. Pistons are a fix for a non existant problome.